Questions: Balance the following skeleton reactions and identify the oxidizing and reducing agents. (Use the lowest possible coefficients. Include states-of-matter under SATP conditions in your answer.) (a) O2(g) + NO(g) → NO3−(aq) [acidic] (b) CrO42−(aq) + Cu(s) → Cr(OH)3(s) + Cu(OH)2(s) [basic] (c) AsO43−(aq) + NO2−(aq) → AsO2−(aq) + NO3−(aq) [basic]

△ Balance the reaction \( O_2(g) + NO(g) \to NO_3^-(aq) \) in acidic conditions and identify the oxidizing and reducing agents. ○ Determine oxidation states. ▷ Analyze the oxidation states of elements in reactants and products to identify changes. ☼ Nitrogen in \( NO \) is oxidized from \( +2 \) to \( +5 \), and oxygen in \( O_2 \) is reduced from \( 0 \) to \( -2 \). ○ Write and balance half-reactions. ▷ Separate the reaction into oxidation and reduction half-reactions and balance them in acidic conditions. ☼ Oxidation: \( NO + 2H_2O \to NO_3^- + 4H^+ + 3e^- \).
Reduction: \( O_2 + 4H^+ + 4e^- \to 2H_2O \).
After combining and simplifying: \( 4NO(g) + 3O_2(g) + 2H_2O(l) \to 4NO_3^-(aq) + 4H^+(aq) \). ○ Identify oxidizing and reducing agents. ▷ Determine which species gains electrons (oxidizing agent) and which loses electrons (reducing agent). ☼ Oxidizing agent: \( O_2 \) (accepts electrons).
Reducing agent: \( NO \) (donates electrons). ✧ Balanced equation: \( 4NO(g) + 3O_2(g) + 2H_2O(l) \to 4NO_3^-(aq) + 4H^+(aq) \).
Oxidizing agent: \( O_2 \).
Reducing agent: \( NO \).

△ Balance the reaction \( CrO_4^{2-}(aq) + Cu(s) \to Cr(OH)_3(s) + Cu(OH)_2(s) \) in basic conditions and identify the oxidizing and reducing agents. ○ Determine oxidation states. ▷ Analyze the oxidation states of elements in reactants and products to identify changes. ☼ Chromium in \( CrO_4^{2-} \) is reduced from \( +6 \) to \( +3 \), and copper in \( Cu \) is oxidized from \( 0 \) to \( +2 \). ○ Write and balance half-reactions. ▷ Separate the reaction into oxidation and reduction half-reactions and balance them in basic conditions. ☼ Reduction: \( CrO_4^{2-} + 4H_2O + 3e^- \to Cr(OH)_3 + 5OH^- \).
Oxidation: \( Cu + 2OH^- \to Cu(OH)_2 + 2e^- \).
After combining and simplifying: \( 2CrO_4^{2-}(aq) + 3Cu(s) + 8H_2O(l) \to 2Cr(OH)_3(s) + 3Cu(OH)_2(s) + 4OH^-(aq) \). ○ Identify oxidizing and reducing agents. ▷ Determine which species gains electrons (oxidizing agent) and which loses electrons (reducing agent). ☼ Oxidizing agent: \( CrO_4^{2-} \) (accepts electrons).
Reducing agent: \( Cu \) (donates electrons). ✧ Balanced equation: \( 2CrO_4^{2-}(aq) + 3Cu(s) + 8H_2O(l) \to 2Cr(OH)_3(s) + 3Cu(OH)_2(s) + 4OH^-(aq) \).
Oxidizing agent: \( CrO_4^{2-} \).
Reducing agent: \( Cu \).

△ Balance the reaction \( AsO_4^{3-}(aq) + NO_2^-(aq) \to AsO_2^-(aq) + NO_3^-(aq) \) in basic conditions and identify the oxidizing and reducing agents. ○ Determine oxidation states. ▷ Analyze the oxidation states of elements in reactants and products to identify changes. ☼ Arsenic in \( AsO_4^{3-} \) is reduced from \( +5 \) to \( +3 \), and nitrogen in \( NO_2^- \) is oxidized from \( +3 \) to \( +5 \). ○ Write and balance half-reactions. ▷ Separate the reaction into oxidation and reduction half-reactions and balance them in basic conditions. ☼ Reduction: \( AsO_4^{3-} + 2H_2O + 2e^- \to AsO_2^- + 4OH^- \).
Oxidation: \( NO_2^- + 2OH^- \to NO_3^- + H_2O + 2e^- \).
After combining and simplifying: \( AsO_4^{3-}(aq) + NO_2^-(aq) + H_2O(l) \to AsO_2^-(aq) + NO_3^-(aq) + 2OH^-(aq) \). ○ Identify oxidizing and reducing agents. ▷ Determine which species gains electrons (oxidizing agent) and which loses electrons (reducing agent). ☼ Oxidizing agent: \( AsO_4^{3-} \) (accepts electrons).
Reducing agent: \( NO_2^- \) (donates electrons). ✧ Balanced equation: \( AsO_4^{3-}(aq) + NO_2^-(aq) + H_2O(l) \to AsO_2^-(aq) + NO_3^-(aq) + 2OH^-(aq) \).
Oxidizing agent: \( AsO_4^{3-} \).
Reducing agent: \( NO_2^- \). ☺ (a) Balanced equation: 4NO(g) + 3O₂(g) + 2H₂O(l) → 4NO₃⁻(aq) + 4H⁺(aq) Oxidizing agent: O₂ Reducing agent: NO(g)

(b) Balanced equation: 2CrO₄²⁻(aq) + 3Cu(s) + 8H₂O(l) → 2Cr(OH)₃(s) + 3Cu(OH)₂(s) + 4OH⁻(aq) Oxidizing agent: CrO₄²⁻ Reducing agent: Cu(s)

(c) Balanced equation: AsO₄³⁻(aq) + NO₂⁻(aq) + H₂O(l) → AsO₂⁻(aq) + NO₃⁻(aq) + 2OH⁻(aq) Oxidizing agent: AsO₄³⁻ Reducing agent: NO₂⁻